Such industrial measuring systems, which are implemented for coordinate positioning of points on a surface, and are formed by a handheld measuring aid in cooperation with a station—such as, in particular, a 6-DoF laser tracker—surveying the measuring aid in space have long been known in the prior art.
Examples of such systems are, for example, described in the patent literature publications WO 1993/07443 A1, WO 1997/14015 A1, WO 2007/124009 A2, or WO 2007/124010 A2, or are also known in the form of the “AT901” laser tracker and “T-Probe” measuring aid products sold by Leica Geosystems AG.
One such handheld measuring aid instrument has, for this purpose, a measuring probe (stylus) for the object surface, which is disposed on a body of the measuring aid, in particular having a tactile ball for physically contacting a measuring point on the object surface (wherein notches, holes, hidden points, etc. should be understood herein as also forming part of the measuring object surface of a measuring object throughout).
Furthermore, instead of, or in addition to, a measuring probe, the measuring aid instrument may also have a handheld scanner equipped for short-range measurements for non-contact surface surveying, wherein the direction and position of the scanner measuring beam used for the short-range measurements are exactly known in relation to the light spots and reflectors disposed on the scanner. Such a scanner is, for example, described in EP 0 553 266 or is also known in the form of the “T-Scan” product sold by Leica Geosystems AG.
In addition, such a measuring aid instrument may also be equipped with further measuring or inspection tools, such as a tool for inspecting or surveying wells (wellbores), or with tools for processing workpieces, e.g. a drill, mill, punch, etc.
Furthermore, visual markings are present which are disposed, forming a pattern, on the body in a defined spatial relationship to one another and in relation to the measuring probe in a marking region. In particular, these visual markings may be provided by passive or active light spots able to be captured by a camera, wherein the markings are in particular formed by reflectors or by LEDs.
The measuring stations (such as laser trackers in particular) to be used together with the measuring aid may then be embodied, to capture these markings, with an optical image capturing unit having a two-dimensional, light-sensitive array, e.g., a CCD or CID camera or a camera based on a CMOS array (or having another pixel array sensor), and with an image processing unit. In particular, the camera may then be installed on the station such that the positions thereof in relation to one another are not variable. For example, the camera is installed on the station such that it is pivotable by a motor about one or about two axes, and can thus track the measuring aid also during movement so that it remains within the camera's field of vision.
A particular example of such measuring stations is the laser tracker with camera. Here, a target point, which is finely targetable and trackable, for such a laser tracker is formed by a retroreflective unit (e.g., a cubic prism or corner cube retroreflector), which is targeted using an optical laser measuring beam of the measuring device. The laser beam is reflected by the retroreflector in parallel back to the measuring device, the reflected beam being captured using a capturing unit of the device. Here, an emission or reception direction of the beam is identified, for example, by means of sensors for angle measurement which are associated with a deflection mirror or a targeting unit of the system. In addition, with the capturing of the beam, a distance from the measuring device to the retroreflector is identified, e.g., by interferometry or by means of runtime and/or phase difference measurement.
For cooperation of a measuring aid with a laser tracker, the measuring aid generally has a retroreflector at a central point of its marking region, which can be automatically targeted, tracked, and surveyed in position in three dimensions with high precision by the laser tracker.
For this purpose, laser trackers of the prior art generally have a tracking surface sensor in the form of a position-sensitive surface detector (such as a PSD or a CCD or CMOS sensor), wherein measuring laser radiation reflected on the target can be detected thereon and a corresponding output signal can be generated. By means of a downstream or integrated electronic system, the output signal can be analyzed and a focal point can be identified, for example. By means of this tracking and fine targeting sensor, a divergence of the point of incidence (focal point) of the captured beam from a servo-control zero point can thus be determined and, on the basis of the divergence, precise targeting or—in the event of movement—repositioning of the laser beam towards the retroreflector can be performed. Capture using the tracking and fine targeting sensor is performed coaxially to the measuring axis, so that the capturing direction corresponds to the measuring direction. The tracking and fine targeting can only be applied after the measuring laser has been at least roughly oriented towards a retroreflective target such that the measuring laser beam is incident on the retroreflector (considered at least somewhere within the beam cross section of the measuring laser beam). After precise targeting, angle and distance measurement is performed—as described above—for the actual surveying of the retroreflector.
The other three degrees of freedom of the measuring aid are determined by recording an image of the markings and corresponding image processing. In particular, the unit guiding the laser beam and the camera can then be formed such that their positions in relation to one another are not variable. For example, the camera is rotatable together with the unit about a substantially perpendicular axis, but is pivotable upwards and downwards independently of the guiding unit and is therefore disposed separately from the optics of the laser beam, in particular. Alternatively, the camera may also be embodied to be pivotable about one axis only. In a further alternative, however, the camera may also be integrally installed together with the beam-guiding unit in a rotatable and pivotable shared housing.
By capturing and analyzing the image—by means of image capturing and processing units—of the visual markings, the relative location of which to one another is known, the orientation of the measuring aid instrument in space may thus be concluded. Together with the determined spatial position of the retroreflector, the position and orientation of the measuring aid in space can therefore be precisely determined absolutely (or at least in relation to the laser tracker)—and therefore ultimately the surface point which is contacted in a tactile or optical manner by the probe of the measuring aid instrument.
As an alternative to the use of a laser tracker as a surveying station for the measuring aid, the station may also be designed such that six-degrees-of-freedom surveying of the measuring aid can also be performed in a solely camera-based manner, as is described in the above-mentioned patent literature publications WO 2007/124009 A2 or WO 2007/124010 A2.
Prior-art measuring aid instruments held in one hand are designed as two-sided in this respect, having a front side to be aligned towards the measuring station, on which the visual markings (and also optionally the retroreflector) are disposed in the marking region—all pointing in a joint direction (->facing perpendicularly away from the front side)—and a rear side, on which a grip handle is disposed to be gripped in an enclosing manner like a rod by a hand (also called a first grip) of a user.
The disadvantage of known measuring aid instruments is that their rigid design and dimensions, in particular length, which are too large for some object spaces, do not always allow to reach the surface or measuring point to be measured in an easily manageable manner or even at all. For example, some measuring points can only be contacted with the measuring ball disposed on the stylus by applying a hand position which is cumbersome for the user and/or using specifically designed holders (the separate use of which requires additional time), or some measuring points may not be contactable at all.